Best Methods & Settings to Prevent Stringing in 3D Printing
- Imagine That
Stringing in 3D printing can be very frustrating and anyone who has operated a 3D printer will have experienced this problem many times. The threads that form on the object are unsightly and can leave residue when removed. Therefore, it is important to avoid stringing as much as possible before printing.
To avoid stringing in 3D printing, the filament must be dry and the nozzle must be clean. Then the following print settings must be optimized: retraction, print temperature, speed and flow rate.
Besides these requirements and settings, there are other strategies to avoid stringing. In this article all solutions are explained in detail.
Stringing is a common problem that can occur in 3D printing. It occurs when the printer extrudes too much plastic, which then hangs in long threads from the nozzle and the object. This can lead to problems such as poor surface quality.
Due to the unwanted extrusion of smallest amounts of filament during movement, stringing occurs between the end of the last extrusion and the beginning of the next one. Thus, stringing would not occur during continuous printing
There are several factors that can contribute to stringing. One is the temperature of the filament: if it is too hot, the plastic may flow too quickly and lead to stringing. Another factor is the speed of the printer: if it moves too fast, the plastic may not have enough time to be retracted before the printer moves on, leading to stringing as well.
But since you can’t avoid having liquid filament in the nozzle, retraction (pulling the filament into the nozzle at the end of an extrusion movement) is critical.
In the following tips you will learn how to make these settings correctly and what other solutions there are to avoid stringing in your 3D printing.
Solutions for Stringing in 3D Printing
There are a few solutions that can help avoid stringing in 3D printing. As just written, most of them modify the extrusion behavior of your 3D printer to avoid the presence of excess material that can pull strings during travel.
However, there are a few other things that are a prerequisite for printing an object without stringing.
Activate Retraction
Stringing occurs in 3D printing when a small amount of material remains at the tip of the nozzle as the extruder moves to a new location. Stringing can be prevented by activating retraction. This pulls the filament back into the extruder before moving it to a new location. Using retraction can be tricky, and it may take a few tries to find the perfect settings. However, this can greatly improve the quality of your 3D prints.
In most slicers, the retraction splits into 2 settings:
The distance by which the filament is pulled back into the nozzle, the “Retraction Distance”.
The speed at which the filament is pulled in, the “Retraction Speed”.
Both settings must be optimized to avoid stringing completely. By default, these settings are already quite good for slicers that have standard profiles (such as Cura). But it still needs some fine tuning and calibration. How to do this and which calibration objects are best suited for this, you will learn at the end of this article.
Retraction Distance
The retraction distance is normally measured in millimeters (mm). The higher this value, the more filament is pulled back into the hotend. This means that you can effectively prevent excess filament from sticking to the nozzle and pulling threads. However, the value must not be too high because otherwise there is too little filament to continue the printing process.
The length of the retraction depends strongly on the printer or extruder used and the respective filament. It is therefore difficult to give good standard values across the board. It is best to start from the values of the standard profile for your printer and the filament used and optimize from there.
Retraction Speed
The retraction speed determines how fast the filament is pulled back. The faster it is pulled back, the less time the filament has to pull the unwanted threads. However, this must also not be too fast, otherwise the pulling force acting on the filament is so great that it could lead to cracks in the filament. This can cause the print to fail or printing errors to occur.
This setting is also found in most standard profiles. If you want to calibrate the retraction distance and the retraction speed, make sure that you only change one value at a time. Otherwise you will not know which changes led to the observed result, which makes further optimization more difficult.
Typical retraction settings (good starting point for optimizations):
Bowden Extruder: 2-6 mm at 30-50 mm/s
Direct Drive Extruder: 0.5-2 mm at 40-60 mm/s
Use Dry Filament
If you are using a filament that tends to absorb moisture, such as PLA, it is a good idea to always use dry filament. Dry filament can improve the quality of a 3D print by reducing the likelihood of stringing, spills, and bubbles.
If the filament has already absorbed moisture, this moisture is released again when the filament is heated. In the case of very moist filaments, bubbles may even form from the evaporated moisture. But even with only slightly moist filaments, the tendency to stringing is significantly increased.
Sometimes inferior filament can also cause stringing. This is because the filament can be inconsistent in diameter and thickness, which leads to problems during extrusion. But material inclusions in impure filament can also mean that extrusion is not uniform and stringing is almost impossible to avoid. So always make sure you buy high quality filament.
Clean the Nozzle
But not only impure filament can lead to stringing, also impurities in the nozzle can cause this printing error. If you have used the nozzle for too long without cleaning it, filament residues always collect in the nozzle. This leads to irregular extrusion, which in turn can lead to stringing and other extrusion problems.
So you should clean your nozzle regularly.
There are different methods how you can clean a 3D printer nozzle. The following list describes all common methods for cleaning a nozzle. The order describes the degree of contamination. Methods for light contaminations are at the top and methods for stubborn residues are at the bottom.
Regular wiping of the hot nozzle: But not only internal contamination of the nozzle can cause stringing, external contamination can also promote such printing errors. Therefore, it makes sense to wipe the nozzle with a paper towel before each print as soon as the printing temperature has been reached. Of course, you have to be careful not to burn your fingers.
Cleaning Filament: Cleaning filament* is a method of using a special filament to clean the nozzle. This filament is designed to remove debris or residue that may have accumulated in the nozzle over time. It is inserted into the printer’s hotend and heated so that any debris that has built up on the sides of the nozzle melts and is extruded with the filament. Regular use is advisable.
Wire brush: Stubborn external contamination and internal contamination directly behind the nozzle opening can be removed with a wire brush. By threading a single wire of the brush into the hole, you can also loosen deeper-seated debris and get it out of the nozzle the next time you extrude filament. The disadvantage of using a wire brush, however, is that you can damage the Nozzle. If the opening of the nozzle is no longer perfectly round and damaged, stringing can occur.
Needle: A fine needle can be inserted into the opening of the hot nozzle to loosen debris inside. This is usually a quick way to dissolve accumulated residues and in combination with cleaning filament a very good method to clean light and heavy residues in your nozzle. There are now special nozzle cleaning kits available that include needles for different nozzle diameters and wire brushes.
Acetone: If the nozzle is very dirty, you can remove it and dissolve the plastic inside in an acetone bath. This is of course a somewhat more drastic method than the ones mentioned so far, but it can loosen a stubborn blockage.
Incineration: This quite popular but extreme variant of cleaning a nozzle consists of heating the nozzle to such a high temperature so that the contaminants inside carbonize so strongly that they can be easily loosened.
Decrease the Print Temperature
There is a “sweet spot” for the temperature of your 3D printer that helps prevent stringing. This point is reached when the filament is just hot enough to flow easily, but not so hot that it becomes too liquid. Filament that is too liquid cannot be controlled with extreme retraction settings and will still drip out of the nozzle during extrusionless movements and cause stringing.
If your prints are pulling a lot of filaments, you should lower the printing temperature by 5-10 °C. The temperature should also not be too low, as this will make the filament more difficult to extrude, resulting in under-extrusion.
Here are the standard temperatures of the most popular filaments:
PLA: 180 – 220 °C
ABS: 200 – 250 °C
PETG: 215 – 235 °C
TPU: 230 – 250 °C
However, these temperatures must be adjusted to the respective printer and the filament used. The best way to find out where the perfect temperature for your filament is in this range is to print a temperature tower.
You can find such objects on portals like Thingiverse or in the Calibration Shapes plug-in in Cura. A temperature tower consists of several layers of a difficult geometry for your 3D printer. With each new layer the temperature is changed slightly, so you can see at the end at which temperature the result is best. I recommend you to do this temperature calibration every time you use a new filament.
Increase the Travel Speed
Stringing is all about preventing excess liquid filament from remaining in the tip of the nozzle as the print head moves from one location to the next without extruding. The speed of this movement also has an impact.
The higher the travel speed, the less time the liquid filament has in the nozzle to flow down and outside the nozzle. With a higher movement speed, you therefore reduce the probability of stringing. However, the speed must not be too high, otherwise under-extrusion can occur and there will be too little liquid filament for the next extrusion movement.
However, the range of the travel speed is different for every printer and can be between 100-200 mm/s. I would recommend you to stay with the default speed that you find in the profile of your printer and adjust the movement speed only if the optimization of the other settings that have been discussed so far have not led to a solution.
Decrease the Flow Rate
Too high a flow rate can lead to over-extrusion in 3D printing because the plastic filament is forced through the extruder nozzle too quickly. This results in too much material being extruded from the nozzle. This can lead to problems such as stringing.
Flow rate, along with print temperature and retraction settings, is one of the three most important print settings you should calibrate at the beginning. The flow rate is a percentage of how much filament is extruded from the nozzle per second. In the slicer, you can usually increase or decrease the rate with a percentage setting.
You can theoretically prevent stringing by reducing the flow rate. However, this would be a relatively blind optimization. You should definitely optimize the retraction settings first and set the print temperature ideally before you change the flow rate.
It is best to calibrate the flow rate. The best way to do this is to print a cube without infill, without top layers and with exactly two walls. After printing, you can measure the wall thickness with a caliper. Depending on how the measured wall thickness differs from the set wall thickness, you have to decrease or increase the extrusion.
Since many print settings are interdependent, it is sometimes necessary to make several passes of the calibrations. For example, if you change the print temperature significantly, it may be necessary to recalibrate the retraction and flow rate.
Disable Z-Hop
With the so-called Z-hop, the nozzle is suddenly pulled upwards for a short distance after the filament has been retracted. This is to prevent the lower tip of the nozzle from colliding with already printed areas during the travel movements.
However, this is usually not necessary at all and often leads to stringing, since the liquid filament is pulled out of the nozzle during the upward movement. So to avoid stringing, you should disable this option and focus on calibrating the important settings for retraction, print temperature and flow rate.
Enable Wiping
By activating wiping, the nozzle is moved to a specific location on the X-axis after each layer so that a brush can be placed there to clean the nozzle. This way you can easily wipe off excess filament before the next layer is printed. This way stringing can be avoided.
However, this method is usually more of a compromise solution. Normally you should be able to avoid stringing with the right settings. With older printers, however, wiping is sometimes the only solution to protect the print object from stringing.
Enable Coasting
In coasting, extrusion is stopped shortly before the end of an extrusion movement. The rest of the line is then printed with the remaining liquid filament in the nozzle.
This measure can be good in case of over-extrusion. The excess material created by over-extrusion is then still used for printing and cannot leave any annoying blobs on your print object afterwards. Stringing then also has less chance to form. The correct setting of coasting is relatively difficult, however, since the distance without extrusion must be set precisely in order to avoid holes.
Replace the Nozzle
As any 3D printer owner knows, a well-functioning nozzle is essential for good print quality. Unfortunately, filament can wear down the nozzle over time, causing damage that leads to uneven extrusion and filament formation. Improper cleaning of the Nozzle with sharp or pointed objects can also cause damage. Therefore, it is important to be careful when cleaning your nozzle.
If the nozzle is damaged, it is best to replace it immediately to improve print quality and avoid stringing. To replace the nozzle, follow these steps:
Heat the old nozzle for three minutes to the print temperature of the filament with the highest temperature range you used. This will help loosen any filament that may be stuck in it.
Carefully remove the old nozzle with pliers and place it on a fireproof surface.
Insert the new nozzle into the hotend and screw it tight.
Use a Smaller Nozzle
To reduce the amount of escaping filament, you can also use a smaller nozzle. The smaller diameter means that there is less liquid filament in the tip of the nozzle that can escape unintentionally.
This will reduce stringing, but will not turn it off completely if you do not use the correct settings.
Activate Part Cooling
Some filaments require cooling during printing. PLA, for example, requires 100% cooling during the complete print, only in the first layers the cooling should be deactivated to avoid poor print bed adhesion.
If cooling is not activated for such filaments, the filament that has just exited the nozzle cools too slowly and can pull threads.
Use a Thinner Bowden Tube
In 3D printers with a Bowden extruder, it can sometimes happen that the stringing is distributed unevenly over the print object. This can be due to the fact that the filament in the Bowden tube has too much play and thus the extrusion becomes uneven.
To avoid this, you should use a Bowden tube with a smaller inner diameter. This restricts the filament’s freedom of movement and prevents it from fluttering back and forth as much and ensures more precise extrusion.
Best Test Objects for Stringing
If you want to test the settings of your 3D printer, various calibration objects are available. For stringing, there are also specialized objects that can be printed very quickly and with little filament.
The advantage of these objects is that they can be printed within a few minutes. Since you will probably have to make several changes to your print settings until you find the perfect configuration, it is important that the object can be printed quickly and uses little filament.
These objects are very suitable for testing the print settings for stringing:
Stinging test in the “Calibration Shapes” plug-in from Cura
Basic Stringing Test by Loohney on Thingiverse (link to object)
When calibrating, make sure you only change one parameter at a time in your print settings so you know where the change came from. If you do this and optimize in small steps, you will quickly find the perfect settings.